A new polar symmetry of huebnerite (MnWO4) with ferrodistortive domains

• Neutron and X-ray diffraction analyzes reveal the polar symmetry P2 for MnWO4.
• Raman mapping shows ferrodistortive domains in its RT paramagnetic state.
• These observations are explained by the hidden polar site C2 for Mn atoms.

Large-size single-crystal samples of huebnerite natural multiferroic MnWO4 were analyzed by neutron and synchrotron X-ray single-crystal diffraction as well as by polarized Raman spectroscopy. Both neutron and X-ray diffraction analyzes reveal polar space-group symmetry P2 for the nuclear structure of huebnerite via the detection of weak reflections h0l (l=odd) forbidden for the gliding plane c. Renninger scans of the reflection 301 on the neutron single-crystal diffractometer RESI (FRM-II) could confirm the absence of the gliding plane c in both para- and antiferromagnetic states of huebnerite. The symmetry breaking could be explained by structure analyzes with neutron single crystal diffraction data at 293 K revealing that two Mn atoms in P2 are displaced independently along the b axis from their equilibrium position at a polar point site, C2 in P2/c. Micro X-ray diffraction and Raman-scattering mapping reveal a ferrodistortive domain texture in the room-temperature paramagnetic state of huebnerite, which is attributed to P2 domain formation through a proper ∼180° rotation about the reciprocal-space axis c*.

Schematic presentation of polar atomic shifts (arrows) in P2 from the respective equivalent sites (spheres) in P2/c at the boundary of two 180°-in-plane micro twins.Figure optionsDownload as PowerPoint slide